Computer networks often use an encryption protocol for encrypting communications between devices. Some examples of encryption protocols are Internet Protocol security (IPSec), Transport Layer Security (TLS), and Datagram Transport Layer Security (DTLS). Encryption protocols sometimes use an initialization vector (IV), also known as a starting variable, as an input to a cryptographic algorithm. The IV is a unique piece of information which ensures that data units being transmitted are encrypted differently, even if the data units are encrypted using the same encryption key and contain identical information. This prevents the underlying data from being inferred by an interceptor of the encrypted data, for example, by recognizing a pattern of encrypted data during repeated transmissions of the same underlying data.
There are many ways to generate an IV. Some cryptographic algorithms require that the IV be random or pseudorandom. Irrespective of how the IV is generated, the IV is subject to size constraints and other requirements imposed by the encryption algorithm, for example, being limited to a certain number of bits. The size affects how many times an encryption key can be used in combination with the IV without compromising security. Thus the lifespan of an encryption key is limited by the IV.